Project 04 · Inventory and planning
How many toys to order for Black Friday and Christmas
If a store orders too little, it runs out right on the busiest days. If it orders too much, the money sits in the warehouse. Here the quantity comes from a formula: site visits, holidays, demographics and the growth of online shopping.
- ×1.50November compared with a normal month in Bulgarian online retail (NSI)
- 51.2%of people in Bulgaria shop online, up 1.4 points in a year (NSI, 2025)
- 27.11Black Friday 2026. The stock has to be in the warehouse before then.
The store is an example, but the market numbers are real and current, with sources. The idea, the choice of data and the checking are mine. The code is written with AI.
The maths, box by box
-
01Visits
43,000
visits per month
This is how many times a month, on average, people came to the store's website over the last year. The number comes from the site's analytics.
Example: the store's own data
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02Buyers
1,247
orders per month
Not everyone who visits buys something. On average, 2.9 of every 100 visitors to an online store place an order.
43,000 × 2.9% = 1,247
Dynamic Yield, online store average, 2024
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03Our toy
100
units in a normal month
The 500-piece building set is in 8 of every 100 orders. People usually buy one.
1,247 × 8% × 1 = 100
Example: the store's own data
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04Black Friday
×1.50
for November
Black Friday is on 27 November and Cyber Monday on the 30th. In Bulgaria November is the strongest month for online shopping: 50% more sales than a normal month.
100 × 1.50 = 150
NSI, online sales in Bulgaria, average of 2023 and 2024
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05Christmas
×1.64
for December
For toys, December is the peak. Toy stores make 13.7% of their yearly sales in December, 1.64 times a normal month.
100 × 1.64 = 164
US Census Bureau, toy stores, 2024. Bulgaria has no separate data for toys.
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06People and the market
+8.8%
more online purchases a year
The population shrinks by 0.22% a year. But the share of people who shop online grows by 2.8%, and each of them buys about 6% more. The normal month is from about half a year ago, so we add the growth since then.
November +4.7% · December +5.4%
NSI: population 2025, online shopping 2025, online sales 2024
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07Forecast
329
units for November and December
This is how many we expect to sell this season: November with Black Friday and December with Christmas.
November 157 + December 172 = 329
Calculated with the formula above
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08Safety stock
+77
units in reserve
The forecast can be off by about 20% a month, which is about 33 units. So we keep a reserve, enough that the stock lasts in 95 of 100 seasons.
1.65 × 33 × √2 = 77
Standard safety stock formula
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09How many to order
276
units = 46 cartons of 6
We need the forecast plus the reserve. 130 units are already in stock and none are on the way. We order the difference, rounded up to whole cartons.
329 + 77 − 130 − 0 = 276
Order-up-to-level formula
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10Deadline
10 November
last day to order
Delivery takes 10 days. While we wait, we will sell about 52 units, plus a reserve of 30. When 82 are left in stock, it is the last moment.
130 in stock, 5.2 a day → we reach 82 on 10 November
Reorder point formula
The whole formula
Four lines of maths
These are the standard formulas of inventory management. Nothing is guessed: every number on the left comes either from the store's data or from official statistics.
- 1
Sales in a normal month
visits × % who buy × % of orders with the product × units per order
- 2
Forecast for the season
normal month × holiday factor × growth (population × online shoppers × purchases per person)
- 3
Safety stock
Z × monthly forecast error × √number of months
Z says how rarely we accept running out: 1.28 for 90 of 100 seasons, 1.65 for 95, 2.05 for 98, 2.33 for 99.
- 4
How many and by when
order = forecast + safety stock − in stock − on order
last moment = when stock falls to: sales per day × delivery days + reserve
Try it yourself
Change the numbers and the pallet rebuilds
Pick a toy or enter your own numbers. Every change recalculates the order.
Order
276 pcs
- Forecast November
- Forecast December
- Safety stock
- Reorder point
What is left at the end of December
The whole order
The same formula for 8 toys
Visits, holidays and the market are shared from the calculator. Each toy has its own stock, delivery time and carton size. A manager can adjust the quantity, approve the row and leave a comment, then download everything for Excel.
| Toy | Forecast Nov + Dec |
In stock | On order | Reserve | Suggested | Order by | Manual adjustment | Approved | Comment | Value |
|---|---|---|---|---|---|---|---|---|---|---|
Adjustments and comments are saved only in this browser.
Where the numbers come from
The online peak in Bulgaria is November, not December
Official NSI data on online sales show how much is bought each month compared with a normal month. Black Friday makes November stronger than Christmas. Toys are different: December is their peak, so for December I use the data for toy stores.
See the numbers
Normal month = the average for the year. The indices are at comparable prices, so they show units, not money.
- Holidays, November ×1.50NSI (National Statistical Institute of Bulgaria), retail trade via mail order, phone or internet, calendar-adjusted indices for 2023 and 2024 (in Bulgarian)
- Christmas for toys ×1.64US Census Bureau: 13.7% of toy stores' yearly sales were in December 2024. census.gov
- 2.9% buyDynamic Yield, average online store conversion rate for 2024. Smart Insights
- Online shoppers 51.2%NSI, internet use by individuals, 2025: +1.4 points in a year. nsi.bg
- Population −0.22%NSI: 6,423,207 people on 31.12.2025, 14,153 fewer than a year earlier. BTA (in Bulgarian)
- Growth +8.8%NSI, online sales in units: the average month of 2024 compared with 2023. The two years are linked through December 2023, which appears in both bulletins.
- The formulasSafety stock, reorder point and order-up-to level. Cleverence
Why not +15%? The Bulgarian E-commerce Association expects the market to grow by 15% in money terms in 2025 (DBR, in Bulgarian). Part of that, though, is higher prices. For the number of toys in the warehouse, what matters is growth in units, so I use the NSI index.
Honestly
What the formula does not know
- The store is an example. For a real store, visits, the product's share and stock come from its own data.
- The holidays are a market average. November is from all online stores in Bulgaria. Christmas for toys is from US stores, because Bulgaria has no separate data.
- We order once for the season. At the peak, suppliers run late and run out. With a fast supplier you can order in parts and hold less.
- Surprises cannot be forecast. If a competitor runs a big promotion or a toy goes viral on social media, no formula will see it. That is why the table has a manual adjustment.